Jared.. Halyards are easy. Height of the mast times 2 plus 5 feet and you are really close to the length of the halyard at the mast. If you are running them to the cockpit, add the distance from the mast base to the cockpit.
If your Catalina is a fractional rig, lay a tape measure along the length of the foresail’s luff. Multiply this length by 2 and add 3 feet. You now have 2 halyard lengths. If you have a Spinnaker, then use the jib or the main halyard length depending if the spinnaker goes to the mast head or is fractional.
This all pretty simply stuff. Tape measure and or the mast height, or the sail luff, plus distance to cockpit if that is where your halyards terminate.